In a related area of study U.S. Pat. No. 4,239,635 discloses carboxylic acid terminated diamides and alkalai metal, ammonium or amine salts thereof which are derived from the reaction of organic polycarboxylic acids and polyoxyalkylene diamines. The diamides have lubricating properties.
There is disclosed in U.S. Pat. No. 4,588,783 an amide-containing hydroxy ethyl carbamate and a coating composition comprising same, the preparation thereof entailing the reaction of an amidoamine and an cyclic organic carbonate.
In U.S. Pat. No. 3,257,342, there is disclosed an epoxy resin composition basically comprising a polyglycidyl ether, an amino-terminated polyamide of a polymeric fatty acid and a compound of the formula: ##STR2## wherein n is an integer of from 1 to 6, R.sub.x, is hydrogen or methyl and each R group is hydrogen or an alkyl.
It is known, as exemplified by U.S. Pat. No. 3,654,370 to prepare polyoxyalkylene polyamines by the reductive amination of a polyoxyalkylene polyol. These polyamines have found utility as curing agents for epoxy resins, as plasticizers, as cross-linking agents and binders for textiles, and as intermediates in the preparation of polyureas. In general, polyoxyalkylene polyamines having molecular weights ranging from about 200 to about 5000 can be prepared by the Yeakey process.
The polyoxyalkylene polyamines of the type disclosed in Yeakey U.S. Pat. No. 3,654,370 are prepared by the oxyalkylation of a polyhydric alcohol. The preferred starting materials are dihydric and trihydric alcohols such as propylene glycol or glycerol and propylene oxide or ethylene oxide. Copolymer polyols of ethylene oxide and propylene oxide are also useful, particularly those containing from about 5 to about 40 wt% of ethylene oxide and corresponding from about 95 to about 60 wt% of propylene oxide.
The molecular weight of the polyol is determined by the number of moles of epoxides that are reacted with the alcohol initiator. Since the addition is random, the final alkoxylation product will not be a pure compound but, rather, will be a mixture of polyoxyalkylene polyols. For example, if the polyol is a polyol prepared by reacting glycerol or trimethylol propane with propylene oxide, using an amount of propylene oxide adequate to provide for an average molecular weight of about 1000, the final propoxylation product will actually be composed of a mixture of polyoxypropylene triols having molecular weights varying from about 800 to about 1200, the molecular weight distribution following a Gaussian distribution curve (sometimes referred to as a sine curve or a Poissan curve). As the molecular weight of the polyol increases, the spread in the molecular weights will also increase. Thus, when the average molecular weight of the triol is about 3000, the deviation will be about .+-.400 molecular weight units so that most of the product will fall within the molecular weight range of about 2600 to about 3400.
As the molecular weight is still further increased, the percentage of free hydroxyl groups in the reaction mixture will decrease because of the added bulk of the already formed polyol, thus making the addition of more propylene oxide groups progressively more difficult. As a practical matter, when the triol reaches an average molecular weight of about 5000, further propoxylation is accomplished only with extreme difficulty and, therefore, the highest molecular weight polyoxypropylene triol obtainable from glycerol of an equivalent triol such as trimethylol propane will have an average molecular weight of about 5000. The 5000 molecular weight polyoxypropylene triols will have a molecular weight distribution of about .+-.1000 so that the actual molecular weight range will be from about 4000 to about 6000. Again, the molecular weight distribution follows a Gaussian distribution curve.
A further complication is encountered during the propoxylation to the higher molecular weights. As the reaction time and temperature are increased to encourage propoxylation, there is introduced a tendency on the part of the propylene oxide to isomerize to allyl alcohol and a tendency on the part of the hydroxypropyl end groups of the polyoxypropylene triol to dehydrate to form a terminal olefin group and water. Both the water and the allyl alcohol are susceptible to oxyalkylation thereby diluting the polyoxypropylene diol with undesired generally low molecular weight diol contaminants derived from the water and monofunctional allyl alcohol propoxylates. From as little as 1% to as much as 10% of the oxypropyl end groups of the triol may dehydrate to form groups with terminal unsaturation in increasing the average molecular weight from about 3000 to about 5000.
When a polyoxypropylene polyol of this nature is reductively aminated in accordance with the procedure of U.S. Pat. No. 3,654,370, comparatively higher temperatures and longer reaction times are required as the molecular weight of the polyol increases. This can result in the cleavage of the polyol to form undesired and unwanted alkyl ether by-products and hydrogenation of the unsaturated groups on the polyol to form propyl ethers.
In copending Application Ser. No. 078,323 the contents of which is herein incorporated by reference, there has been disclosed a process for reducing molecular weight distribution and terminal unsaturation problems by the formation of amidoamines containing terminal primary amine groups which are analogous in function and reactivity to the polyoxyalkylene polyamines of U.S. Pat. No. 3,654,370, but which are characterized by a significantly narrower molecular weight distribution and significantly lower by-product contamination. According to that invention, when the amine is in excess, a primary amine group of the polyamine will preferentially react with each of the carboxyl groups of the di- or tricarboxylic acid, ester or anhydride thereof and be linked thereto through an amide linkage. However, the free primary amine groups will not interact and the reaction will terminate with the formation of an addition product of the polyamine with the carboxylic acid such that the addition product is substantially free from carboxylic groups and contains primarily terminal primary amine groups.
An amidoamine with these improved characteristics would represent a great advance in the art. It has now been discovered that amidoamines with these characteristics exhibit improved properties as epoxy resin curatives in the method of this invention. Other objects may be apparent to those skilled in the art.